U.S. patent application number 13/414113 was filed with the patent office on 2013-09-12 for synchronisation method.
This patent application is currently assigned to CAMBRIDGE SILICON RADIO LIMITED. The applicant listed for this patent is Graham Drinkwater, Nick Jones. Invention is credited to Graham Drinkwater, Nick Jones.
Application Number | 20130235166 13/414113 |
Document ID | / |
Family ID | 49113769 |
Filed Date | 2013-09-12 |
United States Patent
Application |
20130235166 |
Kind Code |
A1 |
Jones; Nick ; et
al. |
September 12, 2013 |
SYNCHRONISATION METHOD
Abstract
A method by which a transmitter and receiver synchronise. The
transmitter and receiver are operable in accordance with a protocol
which mandates that some transmissions are jittered. The method
comprises the transmitter transmitting a pseudo-random seed to the
receiver; determining a jitter value based on the pseudo-random
seed; and transmitting a synchronisation packet to the receiver at
a time determined by the jitter value. The receiver receives the
pseudo-random seed from the transmitter; determines timing of a
receive window for the synchronisation packet based on the
pseudo-random seed; opens the receive window at the determined
time; and receives the synchronisation packet within the receive
window.
Inventors: |
Jones; Nick; (Cambridge,
GB) ; Drinkwater; Graham; (Cambridge, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Jones; Nick
Drinkwater; Graham |
Cambridge
Cambridge |
|
GB
GB |
|
|
Assignee: |
CAMBRIDGE SILICON RADIO
LIMITED
Cambridge
GB
|
Family ID: |
49113769 |
Appl. No.: |
13/414113 |
Filed: |
March 7, 2012 |
Current U.S.
Class: |
348/51 ;
348/E13.075 |
Current CPC
Class: |
H04N 13/398 20180501;
H04J 3/0658 20130101; H04N 13/167 20180501; H04N 13/332 20180501;
H04N 13/30 20180501; H04N 13/194 20180501 |
Class at
Publication: |
348/51 ;
348/E13.075 |
International
Class: |
H04N 13/04 20060101
H04N013/04 |
Claims
1. A transmitter operable in accordance with a protocol which
mandates that some transmissions are jittered, the transmitter
configured to synchronise with a receiver by: transmitting a
pseudo-random seed to the receiver; determining a jitter value
based on the pseudo-random seed; and transmitting a synchronisation
packet to the receiver at a time determined by the jitter
value.
2. A transmitter as claimed in claim 1, wherein the protocol is the
Bluetooth Low Energy protocol.
3. A transmitter as claimed in claim 2, wherein the synchronisation
packet is a Bluetooth Low Energy advertising packet.
4. A transmitter as claimed in any preceding claim 1, wherein the
transmitter is incorporated into a 3D television.
5. A transmitter as claimed in claim 4, wherein the synchronisation
packet comprises timing information indicative of the times at
which the television displays images for reception by left and
right eyes.
6. A method by which a transmitter synchronises with a receiver,
the transmitter and receiver operable in accordance with a protocol
which mandates that some transmissions are jittered, the method
comprising: transmitting a pseudo-random seed to the receiver;
determining a jitter value based on the pseudo-random seed; and
transmitting a synchronisation packet to the receiver at a time
determined by the jitter value.
7. A method as claimed in claim 6, wherein the protocol is the
Bluetooth Low Energy protocol and the synchronisation packet is a
Bluetooth Low Energy advertising packet.
8. A method as claimed in claim 6, wherein the transmitter is
incorporated into a 3D television, and wherein the synchronisation
packet comprises timing information indicative of the times at
which the television displays images for reception by left and
right eyes.
9. A receiver operable in accordance with a protocol which mandates
that some transmissions are jittered, the receiver configured to
synchronise with a transmitter by: receiving a pseudo-random seed
from the transmitter; determining timing of a receive window for a
synchronisation packet based on the pseudo-random seed; opening the
receive window at the determined time; receiving the
synchronisation packet within the receive window; and closing the
receive window following receipt of the synchronisation packet.
10. A receiver as claimed in claim 9, wherein determining timing of
a receive window comprises: determining an expected time of arrival
of the synchronisation packet based on the pseudo-random seed; and
determining a time period of the receive window based on the
expected time of arrival of the synchronisation packet.
11. A receiver as claimed in claim 9, wherein the protocol is the
Bluetooth Low Energy protocol.
12. A receiver as claimed in claim 9, wherein the receiver is
incorporated into a pair of 3D glasses.
13. A receiver as claimed in claim 12, wherein the receiver is
further configured to control a timing of shutters of the pair of
3D glasses based on timing information in the synchronisation
packet.
14. A method by which a receiver synchronises with a transmitter,
the transmitter and receiver operable in accordance with a protocol
which mandates that some transmissions are jittered, the method
comprising: receiving a pseudo-random seed from the transmitter;
determining timing of a receive window for a synchronisation packet
based on the pseudo-random seed; opening the receive window at the
determined time; receiving the synchronisation packet within the
receive window; and closing the receive window following receipt of
the synchronisation packet.
15. A method as claimed in claim 14, wherein determining timing of
a receive window comprises: determining an expected time of arrival
of a synchronisation packet based on the pseudo-random seed; and
determining a time period of the receive window based on the
expected time of arrival of the synchronisation packet.
16. A method as claimed in claim 14, wherein the receiver is
incorporated into a pair of 3D glasses, the method further
comprising: controlling a timing of shutters of the 3D glasses
based on timing information in the synchronisation packet.
Description
[0001] The present disclosure relates to synchronising a
transmitter and receiver. Suitably, the present disclosure is
implemented in a system comprising a 3D television and 3D glasses,
to maintain synchronisation between each shutter of the glasses and
the corresponding image transmitted by the television.
[0002] The revival of 3D entertainment has led to a surge of 3D
televisions entering the domestic market. In conjunction with a
pair of 3D glasses, the 3D televisions enable viewers to perceive a
3D image. Typically, 3D images are conveyed by a 3D television
using stereoscopy and filtered for viewing by liquid crystal (LC)
shutter glasses. Filming in 3D is carried out using two cameras
separated by the average distance between a person's pupils. The 3D
television displays alternate images from the two cameras, one
image intended for the right eye and the other image intended for
the left eye. The rate at which the images alternate between the
right and left image is sufficiently high to give the impression to
a viewer that a continuous 3D image is being displayed rather than
alternate 2D images. The LC shutters "open" and "close"
alternately, such that the right shutter is open when the image for
the right eye is displayed by the 3D television and closed when the
image for the left eye is displayed. Conversely, the left shutter
is open when the image for the left eye is displayed by the 3D
television and closed when the image for the right eye is
displayed. The liquid crystal layer in the LC shutters changes
state on application of a voltage across it. When no voltage is
applied, the LC layer is visibly transparent, and when a voltage is
applied across it the layer turns dark. Thus, the shutters are
"opened" and "closed" by application and removal of a voltage
across the LC layer of the shutters.
[0003] The application and deactivation of the voltage across the
LC layer of the shutters may be controlled by a small device that
can be incorporated into the 3D glasses, for example a Bluetooth
device. In such an application, the controller device in the LC
shutters operates in conjunction with a controller device in the 3D
television to maintain synchronisation of the shutters with the
images displayed by the television. Maintaining synchronisation is
very important. If the shutters are not precisely synchronised with
the images displayed by the television, then one of the shutters of
the glasses may be open when the television switches between the
image intended for one eye and the image intended for the other
eye. This may result in the viewer experiencing flickering and/or a
distorted picture (crosstalk).
[0004] It is advantageous for the power drawn by the controller
device in the 3D glasses to be very low because the 3D glasses are
typically battery operated.
[0005] Thus, there is a need for a low power controller device that
is able to maintain precise synchronisation.
[0006] According to a first aspect of the disclosure there is
provided a transmitter operable in accordance with a protocol which
mandates that some transmissions are jittered, the transmitter
configured to synchronise with a receiver by: transmitting a
pseudo-random seed to the receiver; determining a jitter value
based on the pseudo-random seed; and transmitting a synchronisation
packet to the receiver at a time determined by the jitter
value.
[0007] Suitably, the protocol is the Bluetooth Low Energy
protocol.
[0008] Suitably, the synchronisation packet is a Bluetooth Low
Energy advertising packet.
[0009] Suitably, the transmitter is incorporated into a 3D
television.
[0010] Suitably, the synchronisation packet comprises timing
information indicative of the times at which the television
displays images for reception by left and right eyes.
[0011] According to a second aspect of the disclosure there is
provided a method by which a transmitter synchronises with a
receiver, the transmitter and receiver operable in accordance with
a protocol which mandates that some transmissions are jittered, the
method comprising: transmitting a pseudo-random seed to the
receiver; determining a jitter value based on the pseudo-random
seed; and transmitting a synchronisation packet to the receiver at
a time determined by the jitter value.
[0012] According to a third aspect of the disclosure there is
provided a receiver operable in accordance with a protocol which
mandates that some transmissions are jittered, the receiver
configured to synchronise with a transmitter by receiving a
pseudo-random seed from the transmitter; determining timing of a
receive window for a synchronisation packet based on the
pseudo-random seed; opening the receive window at the determined
time; receiving the synchronisation packet within the receive
window; and closing the receive window following receipt of the
synchronisation packet.
[0013] Suitably, determining timing of a receive window comprises:
determining an expected time of arrival of a synchronisation packet
based on the pseudo-random seed; and determining a time period of
the receive window based on the expected time of arrival of the
synchronisation packet.
[0014] Suitably, the protocol is the Bluetooth Low Energy
protocol.
[0015] Suitably, the receiver is incorporated into a pair of 3D
glasses.
[0016] Suitably, the receiver is further configured to control the
timing of the shutters of the 3D glasses based on timing
information in the synchronisation packet.
[0017] According to a fourth aspect of the disclosure there is
provided a method by which a receiver synchronises with a
transmitter, the transmitter and receiver operable in accordance
with a protocol which mandates that some transmissions are
jittered, the method comprising: receiving a pseudo-random seed
from the transmitter; determining timing of a receive window for a
synchronisation packet based on the pseudo-random seed; opening the
receive window at the determined time; receiving the
synchronisation packet within the receive window; and closing the
receive window following receipt of the synchronisation packet.
[0018] Suitably, determining timing of a receive window comprises:
determining an expected time of arrival of a synchronisation packet
based on the pseudo-random seed; and determining a time period of
the receive window based on the expected time of arrival of the
synchronisation packet.
[0019] Suitably, the receiver is incorporated into a pair of 3D
glasses, the method further comprising: controlling the timing of
the shutters of the 3D glasses based on timing information in the
synchronisation packet.
[0020] The present invention will now be described by way of
example with reference to the accompanying drawings. In the
drawings:
[0021] FIG. 1 illustrates the times at which a receiver expects
packets to arrive, the time at which those packets actually arrive,
and the times at which the receiver is operable to receive the
packets;
[0022] FIG. 2 illustrates a synchronisation method implemented at a
transmitter;
[0023] FIG. 3 illustrates a synchronisation method implemented at a
receiver;
[0024] FIG. 4 illustrates an exemplary computing-based device in
which the synchronisation method of FIG. 2 may be implemented;
[0025] FIG. 5 illustrates an exemplary computing-based device in
which the synchronisation method of FIG. 3 may be implemented;
[0026] FIG. 6 illustrates an example 3D television
[0027] FIG. 7 illustrates the transmission times of packets from a
transmitter;
[0028] FIG. 8 illustrates a synchronisation method implemented at a
transmitter;
[0029] FIG. 9 illustrates a synchronisation method implemented at a
receiver; and
[0030] FIG. 10 illustrates open and closed states of liquid crystal
shutters.
[0031] In the example of the 3D television and 3D glasses being
controlled by respective Bluetooth devices, the Bluetooth device in
the television and the Bluetooth device in the glasses may
communicate in accordance with the Bluetooth Low Energy (BLE)
protocol defined in the Bluetooth Specification version 4.0. This
is preferred to those devices communicating in accordance with the
Bluetooth Basic Rate/Enhanced Data Rate protocol because the 3D
glasses are battery powered and may be required to operate for
lengthy periods, thus minimising the power required for
communication with the television is desirable.
[0032] In accordance with the BLE protocol, streams of advertising
packets are transmitted from the television (acting as a BLE master
device) to the glasses (acting as a BLE slave device) approximately
every 500 ms. These advertising packets comprise timing information
about the timing of the alternating images displayed by the
television. The glasses use this timing information to correct the
timing of the shutters, so as to synchronise the shutters with the
alternating images.
[0033] The BLE protocol in the Bluetooth specification version 4.0
requires that the advertising packets be jittered. This means that
each packet is transmitted at a small deviation in time from the
nominal time at which the receiver expects the packet to be
transmitted. Jittering is required in the BLE protocol to reduce
the likelihood of a transmitted packet colliding with a packet
transmitted from another source that happens to be synchronised to
the nominal time and transmitting on the same frequency.
[0034] As a result of jittering, the Bluetooth receiver in the 3D
glasses does not know exactly when it will receive an advertising
packet from the Bluetooth transmitter in the 3D television. In the
example illustrated in FIG. 1, the receiver expects advertising
packets to be received during time periods 1, 2 and 3. However, as
a result of these packets being jittered by the transmitter, the
receiver actually receives the packets during time periods 4, 5 and
6. Typically, the receiver knows the maximum jitter that can be
applied to the advertising packets. This may be mandated by the
protocol. Alternatively, the transmitter may inform the receiver of
the maximum jitter that it will apply to an advertising packet.
Thus, in order to ensure that the receiver receives each
advertising packet, the receiver is operable to receive a packet
during a receive window which encompasses a time frame allowing for
the maximum jitter preceding and after the expected arrival of the
packet. In other words, the receive window starts at a time equal
to the expected start of the packet minus the maximum jitter time,
and the receive window ends at a time equal to the expected end of
the packet plus the maximum jitter time. The receive window is thus
open for time periods 7, 8 and 9 in FIG. 1.
[0035] The receive window during which the receiver is operable to
receive a packet is significantly longer than the duration of the
received packet. Long receive windows drain the power of a
receiver. In low energy platforms, for example those running off
coin cells (as is typical in the case of 3D glasses), this power
drain is particularly problematic.
[0036] The following description relates to communications between
devices which operate according to a protocol which mandates that
some transmissions are jittered. In an exemplary case, this
protocol is the Bluetooth Low Energy protocol. The example system
described below operates in accordance with the Bluetooth Low
Energy protocol. However, the methods described below apply equally
to any protocol which requires that some transmissions are
jittered.
[0037] In an exemplary Bluetooth Low Energy system, a first device
communicates with a second device. The accuracy of an internal
device clock is limited by the regularity of the frequency of the
crystal oscillator which generates the clocking signal. Hence,
clocks in different devices drift away from each other over time.
This is a particular problem for low energy, low cost devices which
generally operate using relatively inaccurate clocks. To maintain
synchronisation between the devices, the first device transmits
synchronisation packets to the second device. Suitably, these
synchronisation packets contain timing information which the second
device uses to adjust the clocking of its operations. For example,
the timing information may be an indication of the timing of the
clock of the first device. As a result of the clock drift problem,
frequent synchronisation packets are exchanged to maintain
synchronisation.
[0038] In the exemplary Bluetooth Low Energy system,
synchronisation information may be transmitted in advertising
packets. Advertising packets are defined in the Bluetooth
specification version 4.0. The Bluetooth specification requires
that advertising packets are transmitted with a random jitter, i.e.
with a random time offset from the expected time of transmittal.
The value of the jitter is determined by a pseudo-random seed which
is generated by the transmitter. In known methods, the jitter
applied by a transmitter to an advertising packet is not known by
the receiver of the advertising packet. Thus, the receiver opens
its receive window for a long time prior to and after the expected
time of arrival of the advertising packet to ensure that the
jittered advertising packet is received. When the receive window is
open, the receiver processes every signal that it receives, i.e.
amplifies, mixes, demodulates, filters and performs baseband
processing of every signal. All of this processing is power
intensive. When the receive window is closed, the receiver ignores
all signals that it could otherwise receive. Thus, the receiver
mode in which the receive window is open is a high power
consumption mode relative to the receiver mode in which the
receiver window is closed.
[0039] The methods described with respect to FIGS. 2 and 3 reduce
the power consumption of a low energy receiver by reducing the time
for which the receiver has its receive window open. The methods
described with respect to FIGS. 2 and 3 are for illustrative
purposes only. Not all the method steps are necessarily required,
and the steps do not necessarily need to occur in the order
illustrated. In the following description, the transmitter is
incorporated into a device which transmits synchronisation packets
to a receiver, such as the first device described above. Similarly,
the receiver is incorporated into a device which receives
synchronisation packets from a transmitter, such as the second
device described above.
[0040] The operation of the transmitter will now be described with
respect to FIG. 2. At step 200, the transmitter generates a
pseudo-random seed. At step 202, the transmitter transmits the
pseudo-random seed to the receiver. At step 204, the transmitter
determines a jitter value based on the pseudo-random seed. At step
206, the transmitter determines a time to transmit a
synchronisation packet based on the determined jitter value.
Suitably, there is a nominal time of transmittal known to both the
transmitter and the receiver, and the offset of the actual time of
transmittal from that nominal time is given by the jitter value.
For example, the nominal time of transmittal may be the beginning
of a master time slot as defined by the Bluetooth specification
version 4.0. At step 208, the transmitter transmits a
synchronisation packet at the determined time of transmittal.
Suitably, the pseudo-random seed is transmitted to the receiver in
a previous synchronisation packet to the synchronisation packet
whose time of transmittal is dependent on the pseudo-random seed.
The receiver may leave its receive window open following receipt of
the pseudo-random seed in order to capture a succeeding
synchronisation packet that it determines it is about to receive.
Suitably, this previous synchronisation packet is an advertising
packet.
[0041] An exemplary implementation of the operation of the
transmitter will now be described with reference to FIGS. 7 and 8.
In this example, the pseudo-random seed is generated using a shift
register, preferably a linear feedback shift register (LFSR). The
pseudo-random seed is the state of the shift register. The shift
register is initialised with an initial state. The shift register
is clocked prior to the scheduling of an advertising packet
transmission. Following this operation, the shift register outputs
a state. This is illustrated on FIG. 8 as updating the state of the
shift register at step 800. The transmitter determines the jitter
value to be a function of the outputted state. In FIGS. 7 and 8,
this jitter value is referred to as advDelay. For the ith
advertising packet, the advDelay is calculated as:
advDelay(i)=GenAdvDelay(state(i)) (equation 1)
where advDelay(i) is the delay (jitter) applied to the ith
advertising packet's transmission, state(i) is the ith state of the
shift register, and GenAdvDelay is a function which maps the
register state bits to a time delay (jitter). This is illustrated
at step 802 on FIG. 8.
[0042] Suitably, the advDelay represents a value between 0 and 10
milliseconds.
[0043] At step 804 of FIG. 8, the transmitter determines the time
at which to transmit the advertising packet based on the calculated
jitter value. In this example, there is a predetermined minimum
interval between advertising packet transmissions, illustrated as
advInterval in FIG. 7. The time between packet transmissions is
determined to be the addition of the advInterval and the
advDelay:
T_advEvent(i)=advInterval+advDelay(i) (equation 2)
where T_advEvent(i) is the time in between the transmissions of the
i-1th and ith advertising packets, advInterval is the predetermined
minimal interval between advertising packet transmissions, and
advDelay(i) is the delay (jitter) applied to the ith advertising
packet transmission.
[0044] At step 806 on FIG. 8, the transmitter transmits the ith
advertising packet at the determined time T_advEvent(i) relative to
the transmitter's clock. Preferably, the transmitter transmits the
ith register state to the receiver in the ith advertising packet.
The receiver is thus able to calculate the expected time of arrival
of the (i+1)th advertising packet using the ith register state as
described below.
[0045] In the case that a LFSR is used to generate the
pseudo-random seed, the LFSR is preferably implemented in hardware
with associated hardware or software logic. Suitably, the LFSR
produces a maximum-length sequence. It cycles through all possible
states within the shift register excluding the state in which all
the bits are zero. This maximises the randomness of the number
sequence outputted from that LFSR.
[0046] The operation of the receiver will now be described with
respect to FIG. 3. At step 300, the receiver receives a
pseudo-random seed from the transmitter. At step 302, the receiver
determines an expected time of arrival of a synchronisation packet
based on the pseudo-random seed. For example, the receiver may
derive the jitter value from the pseudo-random seed. If the offset
of the actual time of the transmittal of the synchronisation packet
from the nominal time of transmittal is given by the jitter value,
then the receiver determines the expected time of arrival of the
synchronisation packet using the jitter value. At step 304, the
receiver determines the time period of a receive window based on
the expected time of arrival of the synchronisation packet. The
receive window is the time during which the receiver is operable to
receive a signal. At step 306, the receiver opens its receive
window at the determined time period. At step 308, the receiver
receives the synchronisation packet transmitted by the transmitter
within the receive window. At step 310, the receiver closes the
receive window. The receiver closes the window once the
synchronisation packet has been received. Preferably, the receiver
closes the window immediately after receipt of the synchronisation
packet.
[0047] Thus, the receive window is only open during the time period
when the synchronisation packet is being received. This is in
contrast to known methods in which the receive window is open for
much longer to receive the synchronisation packet. Thus, the
methods disclosed herein reduce power consumption at the receiver
compared to known methods.
[0048] An exemplary implementation of the operation of the receiver
will now be described with reference to FIG. 9. This exemplary
implementation is compatible with the transmitter implementation of
FIGS. 7 and 8. In this example, the pseudo-random seed is generated
in the receiver using a shift register, preferably a linear
feedback shift register (LFSR). The pseudo-random seed is the state
of the shift register.
[0049] At step 900, the receiver 900 receives an advertising packet
from the transmitter, referred to in FIG. 9 as the (n-1)th
advertising packet. This advertising packet contains the nth state
of the transmitter shift register. The receiver holds a copy of the
current transmitter shift register state in a store. The receiver
updates the stored transmitter shift register state with the
received nth state at step 902.
[0050] As described above, the receiver also has a shift register.
The receiver operates such that the state of the receiver shift
register is maintained in synch with the state of the transmitter
shift register. At step 904 the receiver clocks the receiver shift
register. Following this operation, the receiver shift register
outputs a state. This is illustrated on FIG. 9 as updating the
state of the shift register at step 904.
[0051] At step 906, the receiver performs a check to see if the
state of the receiver shift register matches the received state of
the transmitter shift register. If it does not, then the receiver
replaces the receiver shift register state with the received
transmitter shift register state. This is calculated as:
If state'(n)!=state(n)
Set state'(n)=state(n) (equation 3)
where state'(n) is the nth state of the receiver shift register,
and state(n) is the nth state of the transmitter shift
register.
[0052] At step 908, the receiver determines the jitter value using
the same method as described above for the transmitter with
reference to FIGS. 7 and 8. The receiver determines the jitter
value to be a function of the current receiver shift register
state. In FIG. 9, this jitter value is referred to as advDelay.
advDelay(n)=GenAdvDelay(state'(n)) (equation 4)
where advDelay(n) is the delay (jitter) to be applied to the next
advertising packet's transmission, state(n) is the nth state of the
shift register, and GenAdvDelay is a function which maps the
register state bits to a time delay (jitter).
[0053] Suitably, the advDelay represents a value between 0 and 10
milliseconds.
[0054] At step 910 of FIG. 9, the receiver determines the time at
which it expects to receive the next advertising packet based on
the calculated jitter value. In this example, there is a
predetermined minimum interval between advertising packet
transmissions, illustrated as advInterval in FIG. 7. The time
between packet receipts is determined to be the addition of the
advInterval and the advDelay:
T_advEvent(n)=advInterval+advDelay(n) (equation 5)
where T_advEvent(n) is the time in between the receipt of the n-1th
and nth advertising packets, advInterval is the predetermined
minimal interval between advertising packet transmissions, and
advDelay(n) is the delay (jitter) applied to the nth advertising
packet transmission.
[0055] At step 910 on FIG. 9, the receiver determines to receive
the nth advertising packet at the determined time T_advEvent(i)
relative to the receiver's clock.
[0056] In the case that a LFSR is used to generate the
pseudo-random seed, the LFSR is preferably implemented in hardware
with associated hardware or software logic. Suitably, the LFSR
produces a maximum-length sequence. It cycles through all possible
states within the shift register excluding the state in which all
the bits are zero. This maximises the randomness of the number
sequence outputted from that LFSR.
[0057] In order to save power, the receiver may not receive one or
more advertising packets. In this case, the receiver still performs
steps 904, 908 and 910 of FIG. 9. However, since it does not
receive an advertising packet it does not update the received copy
of the transmitter's register state, and it does not perform the
check that the receiver and transmitter's respective register
states are synchronised.
[0058] Reference is now made to FIG. 4. FIG. 4 illustrates a
computing-based device 400 in which the described transmitter can
be implemented. The computing-based device may be an electronic
device. For example, the computing-based device may be a
television. The computing-based device illustrates functionality
used for generating a pseudo-random seed and a jitter value, and
for transmitting data.
[0059] Computing-based device 400 comprises a processor 402 for
processing computer executable instructions configured to control
the operation of the device in order to perform the synchronisation
method. The computer executable instructions can be provided using
any computer-readable media such as memory 404. Further software
that can be provided at the computer-based device 400 includes
pseudo-random seed generating logic 406 which implements step 200
of FIG. 2 and jitter generating logic 408 which implements step 204
of FIG. 2. Alternatively, the pseudo-random seed generator and/or
jitter value generator are implemented partially or wholly in
hardware. Data store 410 stores data such as the generated
pseudo-random seed and jitter value. Computing-based device 400
further comprises a transmission interface 412 which implements
steps 202 and 208 of FIG. 2, and a reception interface 414 for
receiving data. Computing-based device 400 also comprises an output
interface 416. For example, the output interface 416 may output
instructions to control an electronics device, for example a 3D
television. Reference is now made to FIG. 5. FIG. 5 illustrates a
computing-based device 500 in which the described receiver can be
implemented. The computing-based device may be an electronic
device. For example, the computing-based device may be a pair of 3D
glasses. The computing-based device illustrates functionality used
for determining the parameters of a receive window, and for
receiving data.
[0060] Computing-based device 500 comprises a processor 502 for
processing computer executable instructions configured to control
the operation of the device in order to perform the synchronisation
method. The computer executable instructions can be provided using
any computer-readable media such as memory 504. Further software
that can be provided at the computer-based device 500 includes
receive window logic 506 which implements steps 302 and 304 of FIG.
3. Suitably, the receive window logic 506 includes logic for
determining the timing of the receive window, for example
pseudo-random seed generating logic and jitter value logic.
Alternatively, the pseudo-random seed generator and/or jitter value
generator are implemented partially or wholly in hardware. Data
store 508 stores data such as the pseudo-random seed received from
the transmitter, and the parameters of the receive window.
Computing-based device 500 further comprises a transmission
interface 510, and a reception interface 512 which implements steps
300 and 308 of FIG. 3. Computing-based device 500 also comprises an
output interface 514. For example, the output interface 514 may
output instructions to control an electronics device, for example
the LC shutters of a pair of 3D glasses.
[0061] In FIGS. 4 and 5 a single computing-based device has been
illustrated in which the described transmitter may be implemented,
and a single computing-based device has been illustrated in which
the described receiver may be implemented. However, the
functionality of the transmitter may be implemented on separate
computing-based devices. Similarly, the functionality of the
receiver may be implemented on separate computing-based
devices.
[0062] In a specific example, the methods described with respect to
FIGS. 2 and 3 are implemented in a system in which a 3D content
source communicates with one or more pairs of 3D glasses to
coordinate the display and reception of a 3D programme. Typically,
the 3D content source is a 3D television. The 3D television may be
configured to play out alternating 2D images (which the viewer
perceives as a continuous 3D image) from a broadcast which the
television has received from an external content provider, for
example a broadcasting station. Alternatively, the 3D television
may be configured to play out alternating 2D images (which the
viewer perceives as a continuous 3D image) from a content memory
located within the 3D television, for example a removable memory
such as a DVD or HDD (hard disk drive) or a fixed memory.
Alternatively, the 3D television may be configured to play out
alternating 2D images (which the viewer perceives as a continuous
3D image) from a content stream received from the internet.
[0063] The transmitter described with respect to FIG. 2 is suitably
incorporated within the 3D television. FIG. 6 illustrates an
example 3D television. 3D television 600 incorporates
computing-based device 400 from FIG. 4. 3D television 600 further
comprises processor 602 for processing computer executable
instructions configured to control the operation of the television.
3D television 600 further comprises a content store 604 for storing
the sequence of 2D images to be displayed. 3D television 600
further comprises display 606 for playing out the sequence of 2D
images received from the content store 604 under the control of
computing-based device 400. Optionally, 3D television 600 also
comprises inputs 608 suitable for receiving user input, for example
to select the programme being played out.
[0064] The receiver described with respect to FIG. 3 is suitably
incorporated within a pair of 3D glasses. Suitably, the 3D glasses
have liquid crystal shutters which change state from a visibly
transparent state to a visibly dark state on application of a
voltage across the liquid crystal layer in the shutters. This is
illustrated in FIG. 10. Circuits (a) and (b) show application of a
voltage differential across the LC shutter, which results in the
light being visibly blocked by the liquid crystal layer. Similarly,
the liquid crystal shutters change state from a visibly dark state
to a visibly transparent state on removal of the voltage across the
liquid crystal layer. This is illustrated in FIG. 10. Circuits (c)
and (d) show no voltage differential across the LC shutter, which
results in the light being visible through the liquid crystal
layer. Hence, the shutters are "opened" and "closed" by application
and removal of a voltage across the LC layer of the shutters.
[0065] The switches in the circuits shown in FIG. 10 are suitably
electronically controlled using MOSFETs driven by Programmable
Input/Output signals. Suitably, the receiver controls the
activation and deactivation of the voltage across the LC layer of
each of the left and right shutters. Suitably, the receiver
controls the activation and deactivation of the shutters based on
timing information received in a received synchronisation packet,
such that the shutter for the right eye opens when the image for
the right eye is being displayed by the television and closes when
the image for the left eye is being displayed by the television,
and such that the shutter for the left eye opens when the image for
the left eye is being displayed by the television and closes when
the image for the right eye is being displayed by the
television.
[0066] Suitably, the synchronisation packets transmitted by the
transmitter comprise timing information indicative of the times at
which the television will display images for reception by left and
right eyes.
[0067] Thus, the receiver in the 3D glasses uses the timing
information in the synchronisation packets to accurately
synchronise the opening and closing of the shutters with the
alternating images displayed by the 3D television. The receive
window of the receiver in the 3D glasses is open for a shorter
period than in known glasses and thus the power consumption of the
glasses is reduced compared to known glasses.
[0068] The advertising packets defined in the Bluetooth
specification can be broadcast packets. Suitably, the transmitter
in the 3D television broadcasts the advertising packets to a
plurality of pairs of 3D glasses, each comprising a receiver as
previously described. Each receiver synchronises to the transmitter
in the 3D television by implementing the method described with
respect to FIG. 3. Thus, a plurality of viewers wearing 3D glasses
are able to watch the same 3D display on the television and remain
fully synchronised without requiring the transmitter in the
television to synchronise with each receiver in the glasses
independently.
[0069] The applicant draws attention to the fact that the present
invention may include any feature or combination of features
disclosed herein either implicitly or explicitly or any
generalisation thereof, without limitation to the scope of any of
the present claims. In view of the foregoing description it will be
evident to a person skilled in the art that various modifications
may be made within the scope of the invention.
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